Once again you forgot to read on to verse 20.
Acts 3:20 and that He may send Jesus, the Christ appointed for you,
See there? "that He may send Jesus". Wasn't Jesus already sent? Still Peter is talking about "may send Jesus"? Let's look back and put that with verse 19.
Acts 3:19 "Therefore repent and return, so that your sins may be wiped away, in order that times of refreshing may come from the presence of the Lord; 20 and that He may send Jesus, the Christ appointed for you,
Think about that. Peter is talking to them after the death and resurrection of Jesus. Yet he makes the comment "may send"? And that "times of refreshing may come from the presence of the Lord"? He's talking about when Jesus returns to set up His Kingdom after the tribulation. That's when the Jews will see "times of refreshing from the presence of the Lord".
>>then at what point did Peter and the 11 shift from the kingdom message and take up the grace message?<<
I don't think Peter and the 11 ever really "shifted" did they? Their focus was always on the Jews/Israel and the coming time when Jesus would set up His Kingdom. Now that's not to say they didn't also preach grace as Peter did mention in his sermon at Pentecost but look at his words in Acts 2 starting with verse 17.
Acts 2:17 And it shall come to pass in the last days, saith God, I will pour out of my Spirit upon all flesh: and your sons and your daughters shall prophesy, and your young men shall see visions, and your old men shall dream dreams: The phrase "in the last days" is talking about the time of the tribulation after the "church" has been taking out of the world and God is once again dealing with the nation of Israel prior to Jesus setting up His "Kingdom" on earth.
>>Also, at what point did Paul cease teaching or preaching the kingdom gospel?<<
Paul didn't "cease preaching the kingdom gospel". He was the one who differentiated between the "dispensation" of grace" and the attention again being given the people of Israel after "the fullness of the Gentiles".
I want to point out a couple of statements in your referenced passage from 1 Peter 1.
"reserved in heaven for you"
What's "reserved in heaven"? Isn't it Jesus who will return to set up His kingdom on earth for 1000 years?
"ready to be revealed in the last time"
Again, that "revealed in the last time". That's again referencing the time Israel turns to Christ just prior to Him setting up His kingdom on earth.
"the sufferings of Christ and the glories that would follow"
What "glories that would follow? Isn't the the glories that will be given the saved Jews/Israelites at the end of time with their King and Messiah sitting on the throne of David in Jerusalem?
The above is key so would like clarification. Did Paul preach two gospels; one of grace to the Gentiles and one of the kingdom to the Jews? If so how long did he teach/preach two different gospels? Or did he not at all preach the kingdom gospel?
On your other comments. Taking your Acts 2, 3 and 1 Peter 1 comments in stride, you paint two distinct classes of believers not just in end times but in the early church. At what point did this message of the physical kingdom end for good in the early church so that the gospel of grace could be realized for not only "Greek" but also for Jew?
Based on the above, how do you explain the same Holy Spirit falling on Jews and the Diaspora Jews on Pentecost and then later on Samaritans, Romans, Greeks... (Gentiles).